In the manufacturing of color negative photographic printing papers, at least three light sensitive emulsion layers are used to capture the photographic image, i.e., red, green, and blue. Frequently, the blue sensitive emulsion is placed at the bottom of the light sensitive multilayer coating pack. In this layering order, less light is available to the bottom blue layer because of the light scattering and absorption occuring in the layers above.
The incandescent lamp used for exposing the paper is low in its energy output in the short wavelength region (blue) of the visible spectra. This further reduces the energy impinging on the blue layer.
The color negative film through which the light is exposed onto the photographic paper has a yellowish brown tint (as a result of the processing used for development). This yellowish background filters out blue light causing a further diminution of blue light arriving at the bottom layer.
Still, in recent developments in the art of manufacturing color photographic paper, there is a need to improve the color reproduction of the original scene as captured in the color negative film. One way of achieving such an improvement is to employ a shorter blue spectral sensitizing dye that better matches the blue sensitization of the original film (See U.S. Ser. No. 245,336 filed May 18, 1994). As a result, the sensitivity of the blue emulsion is further pushed towards the shorter wavelength region where less light energy is available.
Consequently, there exists a need to manufacture a blue sensitive emulsion that has a high sensitivity (speed) in order to overcome the light deficiency and to capture the fidelity of the original color image.
Photofinishers also desire short processing times in order to increase the output of color prints. One way of increasing output is to accelerate the development by increasing the chloride content of the emulsions; the higher the chloride content the higher the development rate. Furthermore, the release of chloride ion into the developing solution has less restraining action on development compared to bromide, thus allowing developing solutions to be utilized in a manner that reduces the amount of waste developing solution.
Another factor to be considered when designing a color paper is print quality such that it is pleasing to the eye both in color and contrast. A color paper with high contrast gives saturated colors and rich details in shadow areas.
The use of poly(ethylene) oxide, PEO (also known as polyoxyethylene) in the photographic industry has been well documented. It is a polymeric substance represented by R--(OCH.sub.2 CH.sub.2).sub.n OH, where R may be H or alkyl or substituted alkyl with the number of carbon atoms ranging from 1 to 25, land n may vary from 1 to 40. It is known that PEO either in the emulsion or added to the developer can accelerate development under some conditions and retard under others (U.S. Pat. No. 2,441,389). The degree of acceleration or retardation depends on the developing agent, the composition of the photographic emulsion, the composition of the developer solution, and the type of PEO used. These factors have been extensively investigated and disclosed in the art (James, T. H. in The Rate of Development; James, T. H., Ed.; The Theory of the Photographic Process, 4th edit. chapter XIV, Macmillan: New York, 1977, pp 424-426). Other pertinent patents on PEO include German Patent 1 037 851, U.S. Pat. No. 2,423,549, U.S. Pat. No. 2,743,180, U.S. Pat. No. 2,704,716, U.S. Pat. No. 2,708,162, U.S. Pat. No. 2,848,330, and U.S. Pat. No. 3,397,987. It can only be concluded that apriori, the effect of PEO on a given emulsion with a specific PEO in a given developer, cannot be anticipated from prior art. Development accelerators of the poly(alkylene oxide) type are disclosed by Blake et al U.S. Pat. Nos. 2,400,532 and 2,423,549, .Blake U.S. Pat. No. 2,441,389, Chechak et al U.S. Pat. No. 2,848,330, Howe U.K. Patent 805,827, Piper U.S. Pat. Nos. 2,886,437 and 3,017,271, Carroll et al U.S. Pat. Nos. 2,944,900 and 2,944,902, Dersch et al U.K. Patent 1,030,701 and U.S. Pat. Nos. 3,006,760, 3,084,044 and 3,255,013, Beavers U.S. Pat. No. 3,039,873, Popeck et al U.S. Pat. No. 3,044,874, Hart et al U.S. Pat. No. 3,150,977, Willems et al U.S. Pat. Nos. 3,158,484, 3,523,796 and 3,523,797, Beavers et al U.S. Pat. Nos. 3,253,919 and 3,426,029, Goffe U.S. Pat. No. 3,294,540, Milton U.S. Pat. No. 3,615,519, Grabhoefer et al U.S. Pat. No. 3,385,708, Mackey et al U.S. Pat. Nos. 3,532,501 and 3,597,214, Willems U.S. Pat. No. 3,552,968, Huckstadt et al U.S. Pat. No. 3,558,314, Sato et al U.S. Pat. No. 3,663,230, Yoneyama et al U.S. Pat. No. 3,671,247 and Poller et al U.S. Pat. No. 3,947,273 and U.K. Patent 1,455,413.